OOOOHH, so not just some random person walking down the street, you're actually referring to someone operating a public business, and that person being allowed to decide that they don't want to deal with an entire group of people, even though they deal with everyone else, and the government saying that it's ok for them to do that if that's what God told them to do.
Specifically, that's NOT what they do. From my linked article:
the Huguenins' photography business does serve gay and lesbian clients, just not same-sex weddings.
So it's actually very close to what you say. They provide photographs to all classes of people, but they don't provide photography services for certain events: Gay Marriages, Photographs depicting violence, and nude maternity photos.
In other words, the Huguenins are being sued for being required, by law, to attend and participate in a gay wedding.